The invention relates to a method for determining the content materials of a liquid medium using a light source and an optical detector, for example a spectrometer, with at least one measuring beam and at least one reference beam, and whereby at least one measuring beam is directed through the medium that is to be analyzed and at least one reference beam is directed outside of the medium that is to be analyzed.
The probes, measuring in a photometric manner and which are used in the context of such methods, for the “in situ” use in order to determine the content materials of a liquid, for example of river water or of waste water, usually have a light source and an optical detector, for example a spectrometer, with at least one measuring beam and at least one reference beam, and whereby the light of the light source is fanned, if need be, and brought into focus in one essentially parallel beam by way of at least one optical lens.
Spectrometers featuring measuring and reference beams are known from DE 3 248 070-A1 and DE 3 340 570-A1; regarding “in situ” measurements from AT-A2167/99.
DE 3 248 070 A1 relates to an infrared analyzer with a beam that is divided and directed, on the one hand, through a measuring cuvette and, on the other hand, through a reference cuvette.
DE 3 340 570 A1 relates to a spectral photometer, which also provides for the division of the beam into a measuring beam and a reference beam, but here with a temporal offset by a rotating mirror. In this instance, a joint detector is envisioned for both beams. In order to ensure that both partial beams have the same wavelength, the frequency shift in the monochrometer is only effected when no measurement occurs.
Both apparatuses are set up discretely, i.e. they are comprised of several units, that may, though, have a joint housing which, however, does not allow for the apparatus as a whole to be immersed into the fluid that is to be measured; but it is necessary to place any samples that are taken in the apparatus using the corresponding containers such as cuvettes, etc.
AT-A 2167/99 relates to a spectral probe for “in situ” measuring. With this probe the measuring beam is directed through a light-transparent window into the fluid that is to be examined and then, through another light-transparent window, redirected into the probe. The reference beam is only directed on the inside of the probe without passing through the windows that touch the fluid.
Also available are optical probes that are immersed in the fluid and that measure “in situ.” But these probes do not work spectrometrically; instead their function is limited to only one wavelength or the integral of a wave range, and they measure the opacity of the fluid or the concentration of an individual special content material. The latter named methods are not able to examine the optical quality of the windows because the reference beams, insofar as they are available, run on the inside of the housing. But the optical quality of the windows has an influence that is quite essential relative to the quality of the measurement because, primarily when measuring waste water, window discolorations and bacterial growth cannot be avoided and even with mechanical cleanings, such as by means of window wipers, it is not possible to guarantee the optical quality of the window.
Moreover, with the aforementioned systems, it is not possible to separate content materials that are mechanically settable, such as activated sludge in the activated sludge lagoon of a water treatment plant, from waste water. Thus, settlement units must be arranged in series upstream of the systems in order to measure the activated sludge whereby, however, in particular the value of an “in situ” measurement is lost.
The need for “in situ” measurements of water types, in particular of river water, waste water and process waters in pipes, is increasing. Using spectral photometry, it is possible to measure characteristics, such as e.g. nitrate and the SAK (spectral absorption coefficients) directly. In combination with mathematical optimization methods that are available today, such as e.g. neuronal nets, it is possible to provide with a correspondingly qualified measuring technique sum parameters, such as e.g. TOC and CSB, as substitute parameters.
Thus, the object of the invention consists in configuring the method and the apparatus in such a way that measuring and reference beams have to pass through the same optical glasses, with the same opacities and contaminations, that a measuring chamber is created that will allow for the evacuation of settable materials from the area of the measuring and reference beams.